1. Field of the Invention
The present invention relates to a PTT (Push To Talk) call service method for a mobile communication terminal, and more particularly, to a method for transmitting an SMS message to other participants during a PTT call service.
2. Background of the Prior Art
Mobile communication systems can be classified into audio service systems and data service systems according to their utilization. A representative example of a mobile communication system is a Code Division Multiple Access (CDMA) system. In the CDMA system, an International Standard (IS-95) system supports only an audio service. With recent developments in communication technology, mobile communication systems have made progress toward a high-speed data service. For example, a CDMA2000 1x system supports both an audio service and a high-speed data service. Mobile communication systems are also developing toward a multimedia service and a Push To Talk (PTT) service, as well as a regular one-to-one voice communication.
In using the PTT service, a user logs in and selects a group or a member who he or she wants to communicate with among groups of co-workers or friends or others displayed on a display. Then, the user requests and initiates a PTT call service. After a one-to-one or intergroup communication path is set on a network that can provide the PTT service, the call can be in service through the set communication path. Specifically, unlike a general phone, the PTT service can directly provide a call service by pressing a PTT button. Further, since a group call with more than three participants is possible, the user can economically benefit from it.
A PTT service using a Session Initiation Protocol (SIP) in the mobile communication system is called a Push to Talk over Cellular (POC). Hereinafter, the POC service and the PTT service will be used interchangeably.
FIG. 1 is a block diagram of a network configuration that provides a POC service in a mobile communication system. The network configuration includes a User Agent (UA) 10 for supporting a POC service and providing wireless access based on a CDMA2000 1x standard, a CDMA2000 1x Access Network (AN) 20 for transmitting/receiving packets to/from the UA 10 over a wireless channel, a Packet Data Service Node (PDSN) 30 for connecting the AN 20 with an Internet Protocol (IP) network 40 using an IP, and a POC server 50 connected to the IP network 40 to manage a POC session and relay a packet from a person talking to a plurality of listeners.
In such a POC service network, an SIP may be used as a POC service protocol for a signaling transmission. A Real-time Transport Protocol (RTP) may be used for real-time packet transmission. The SIP is an end-to-end and server-client signaling protocol, and exchanges necessary session information before a call starts, and removes session information after the call ends.
As described above, the POC service has an advantage in that voice data can be transmitted to a plurality of UAs at the same time, but has a disadvantage in that only one person can speak at a time, such that any person, except the person talking, trying to speak cannot even in an urgent situation. The reason is that unlike a general phone service the PTT service provides only a one-way communication.